Gallium nitride-based III-V nitride, which is attracting attention as an excellent blue light emitting element, is put into practical use in light emitting diode field, and expected also as an optical pickup blue-violet semiconductor laser element. In a process for growing a gallium nitride single crystal by Na flux method, mixed gas of nitrogen and ammonia is used with an atmospheric pressure of 10 to 100 atms, for example, in Japanese Patent Publication (Laid-Open) No. 2002-293696A. In also Japanese Patent Publication (Laid-Open) No. 2003-292400A, the atmospheric pressure during the growth is 100 atm or less, with 2, 3 and 5 MPa (about 20 atm, 30 atm and 50 atm) being used in working examples thereof.
On the other hand, the present inventors disclosed a method for efficiently growing a gallium nitride single crystal under a specific condition by use of a hot isostatic pressing (HIP) apparatus in Japanese Patent Application No. 2004-103093 (WO2005/095682 A1).
In “Growth of Large/Low-Dislocation GaN Single Crystal by LPE Growth” by Kawamura et al. of “Journal of Japanese Association for Crystal Growth” Vol. 32, No. 1, 2005, it is described that when a GaN single crystal is grown by Na flux method, the GaN single crystal is liable to black due to existence of nitrogen defects.